Ground following map and navigation instrument



Aug. 26, 1952 F. E. BEST 2,608,094

GROUND FOLLOWING MAP AND NAVIGATION INSTRUMENT Original Filed Aug. 15, 1941 14 Sheets-Sheet 1 Aug. 26, 1952 F. E. BEST 2,608,094

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F. E. BEST Aug. 26, 1952 GROUND FOLLOWING MAP AND NAVIGATION INSTRUMENT 14 Sheet-s-Sheeti Original Filed Aug. 15, 1941 .NVENTOR.

Aug. 26, 1952' F. E. BEST 2,508,094

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Aug. 26, 1952 F. E. BEST 2,503,094

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Aug. 26, 1952 F, 'E, BEST 2,608,094

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F. E. BEST Aug. 26, 1952 GROUND FOLLOWING MAP AND NAVIGATION INSTRUMENT v 14 Sheets-Sheet 14 OriginaIFiled Aug. 15, 1941 FIG. 47.

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' INVENTOR Patented Aug. 26, 1952 GRQUND FOLLOWING MAP AND NAVIGATION INSTRUMENT Frank Ellison Best, Indianapolis, Ind.

Original application August 15, 1941, Serial No.

407,087. Divided and this application Novemher 4, 1946, Serial No. 707,739

. 9 Claims. 1 Nature and objects of invention This is a divisional application of my co-pend-- ing application on Ground Following Map and Navigation Instrument, filed August 15, 1941, Serial No. 407,087 now abandoned.

My invention relates to ground following map means adapted for use in controlling the navigation of vehicles of all types such as aircraft, space ships, boats, cars, tanks and the like.

The principal object of this invention is to provide automatic means, in one compact unit, for receiving, composing and advantageously diuplaying certain important navigation information and data desired by the navigator or operator of a moving vehicle, or by ground operators assisting in the navigation of the vehicle.

Ancther'object is to providea composite, variably-scaled image of the surface configurations of the ground round about and beneath a craft, of a distance scale image giving the correct scale in miles or kilometers from the location of the craft on said image, and of a direction-indicating image showing the line of travel and deviation from the heading due to drift of said craft relative to said surface configurations image. This is propriate markings and used in making declination corrections, preferably contribute to the desired result, and cardinal congruence between image and surface configurations is preferably maintained by automatic repeater motor means following a master compass.

In'the device that I have selected to illustrate my invention, I have purposely chosen simple, rudimentary means that are easy to draw and illustrate and I have stayed away from the more highly technical and involved means that I prefer to generally employ inpractice. For instance, I am purposely selecting a map plate that can be made by the photographic process and an ordinary light projector rather'than the more elaborate radar or television means that I will often preferably employ. I also use a simple, though antiquated, light responsive means, but one that lends itself to sinuole illustration and description.

Other objects will be apparent from a study "of the following deseription and the concluding claims;

In the drawings,

Figure 1 is a plan view showing the instrument board of a ground following map and navigation instrument that is constructed in accordance with my invention.

Fig. 2 is a vertical sectional view of the same takensubstantially on broken line 22 of Figs. 1, 3, 12 and 14, parts being shown in elevation.

Fig. 3' is a horizontal sectional view taken substantially on broken line 3-3 of Fig. 2 parts being shown in plan.

Fig. 4 is a diagrammatic view showing the relation of the various units of the device to each other and showing in a general way the electrical connections.

Fig. 5 is a detached view in vertical section taken substantially on broken line 5'5 of Fig. 6 showing a master'compass embodied in my invention. c

Fig. 6 is a fragmentary sectional view of said master compass taken substantially on broken line 66"0f Fig. 5.

Fig. '7 is afragmentary sectional development of a light shutter taken substantially on broken line 1--l of Fig; 6;

Fig. 8 is a diagrammatic view or" a repeater motor embodied in this invention taken substantially on broken line 88 of Fig. 9.

Fig. 9 is a diagrammatic view with parts in section of said repeater motor taken substantially on broken line. 9-9 of Fig. 8.

Fig. 10 is a diagram of the repeater motor of Figs. 8 and 9 and'parts connected therewith.

Fig. ll'is a fragmentary sectional view taken substantially on broken line Hl! of Fig. 1 showing true north correction devices.

Fig. 12 is a cross section taken substantially on broken-line l2-|2 of Figs. 2 and 13 showing a distant scale and direction plate and means for rotatively moving the same.

Fig. 13 is a fragmentary sectional view taken substantially on broken line !3l 3 of Fig. 12.

Fig. 14 is a cross section taken substantially on broken line I 4'l,4 of Fig. 2 showing plate elevating means. j

Fig. 15 is a fragmentary, sectional view, taken substantially onbroken line l5-l5 of Fig. 14, showing parts of the plate elevating means and showing electrical control means diagrammatically. Y.

Fig. 16 is a fragmentarysectional view of parts of the map frames, taken substantially on broken lines li5l6 of Figs. 2 and 17, parts being shown in relief, certain parts being in relatively exploded relation.

Fig. 17 is a fragmentary sectional view of parts of the map frames, taken substantially on broken lines I7l'l of Figs. 3 and 16, parts being shown in relief, certain parts being in relatively exploded relation.-

Fig. 18 is a fragmentary sectional view, with parts in elevation, taken substantially on broken line l8-l8 of Fig. 19, showing parts of the map frame.

Fig. 19 is a fragmentary sectional view, with parts in elevation, taken substantially on broken lines I9l9 of Figs. 18 and 20.

Fig. 20 is a fragmentary sectional view with parts in elevation, taken substantially on broken lines 2020 of Fig. 19.

Fig. 21 is a fragmentary sectional view, taken substantially on broken line 2 I2l of Figs. 3 and 16, showing means for moving a north and. south map frame.

Fig. 22 is a fragmentary sectional view, taken substantially on broken line 22-22 of Fig. 3, showing a bracket for supporting a motor that moves the north and south map frame and showing parts of the electrical conductor means for said motor. I

Fig. 23 is a fragmentary sectional view, taken substantially on broken line 23-23 of Fig. 3.

Fig. 24 is a fragmentary sectional view, taken substantially on broken line 24--24 of Fig. 3, showing means for moving an east and west map frame.

Fig. 25 is a fragmentary plan view of a frame member and electrical conductor means connect ed therewith, taken on line 2525, Fig. 26.

Fig. 26 is a fragmentary sectional view taken substantially on broken line 26-26 of Fig. 25.

Fig. 27 is a vertical sectional view on broken line 212'| of Fig. 28 showing an air speed device constructed in accordance with this invention.

Fig. 28 is a vertical sectional view of. the same taken substantially on broken line 28-28 of Fig. 27.

Fig. 29 is a horizontal section taken substantially on broken line 29-49 of Fig. 28.

Fig. 30 is a fragmentary cross-sectional view of a light responsive cell used in this air speed device, said section being taken on line 30-30 of Fig. 31.

Fig. 31 is a fragmentary diagrammatic sectional view of said light responsive cell said section being taken on line 3I3l of Fig. 30..

Fig. 32 is a vertical sectional view, taken substantially on broken line 3232 of Fig. 33 showing a direction finder and ground speed device constructed in accordance with my invention, parts being diagrammatically shown.

Fig. 33 is a reduced view partly in section and partly in plan taken substantially on broken line 33-33 of Fig. 32.

Fig. 34 is a detached reduced perspective view of a grid cell frame and shaft embodied in the invention. V

Fig. 35 is a diagrammatic view of a four segment light grid cell embodied in the device shown in Figs. 32, 33 and 34 showing the electrical connections of the same to motors which control the rotative movement of said cell and also to a repeater motor used in a ground speed arithmetical scale-to-logarithm device.

Fig. 36 is a sectional view, on broken line 36-36 of Figs. 1 and 37, showing an operator-controlled logarithmic wind velocity devic constructed in accordance with this invention.

Fig. 37 is a sectional view with parts in plan taken substantially on broken line 31-37 of Fig. 36.

Fig. 38 is a diagrammatic view of a logarithmic light actuated grid or cell embodied in the wind velocity device shown in Figs. 36 and 37.

Fig. 39 is a fragmentary sectional detail, on a larger scale than Figs. 36 and 37, of the logarithmic light responsive cell embodied in Figs. 36, 37 and 38.

Fig. 40 is an axial sectional view of a device for finding the algebraic sum of two variable values, parts being shown diagrammatically.

Fig. 41 is a fragmentary view of a light shutter used in the device shown in Fig. 40.

Fig. 42 is an axial sectional view of a device for converting values represented in terms of arithmetical scale to values represented in terms of motion, parts being diagrammatically shown.

Fig. 43 is a sectional view taken substantially on broken line 43-43 of Fig. 42.

Fig. 44 is a diagrammatic view of a fragment of a light grid cell embodied in Figs. 42 and 43.

Fig. 45 is an axial sectional view of a manual map mover embodied in this invention, certain electrical controls being diagrammatically shown.

Fig. 46 is a diagrammatic view of a fragment of a light grid cell used in the device shown in Fig. 45.

Fig. 47 is an axial sectiona1 view of a ground speed scale-to-log device embodied in this invention, parts that are connected therewith being diagrammatically shown.

Fig. 48 is a diagrammatic developed view of a fragment of a logarithmic light grid cell used in the device shown in Fig. 47.

Fig. 49 is a fragmentary sectional view showing parts of a ground speed device that is operated by the values provided by the scale-to-log device shown in Figs. 1, 47 and 48.

Fig. 50 is a fragmentary sectional view taken on lines 50-50, Fig. 1, showing parts of an airspeed device that is operated by values provided by a scale-to-log device like that shown in Figs. 47 and 48 which is connected with a fixed airspeed device.

Fig. 51 is a fragmentary diagrammatic development of a cylindrical light responsive grid embodied in the housing and light projector structure shown in Fig. 2, said view being taken on line 5l-5l of Fig. 52.

Fig. 52 is a fragmentary sectional view on a larger scale of said grid, taken on line 52-52 of Figs. 20 and 51.

Like reference numerals designate like parts throughout the several views.

General description Before describing the various units embodied in this ground following map and navigation instrument I will describe in a general way the set up as shown diagrammatically in Fig. 4. I will then describe the several units and explain their cooperation in the combination diagrammatically shown in Fig. 4.

In a general way the apparatus shown diagrammatically in Fig. 4 comprises a master magnetic compass I00 controlled by the earths magnetic field. This master compass I00 is electrically connected with and controls true north follower devices lfll having manually adjustable means provided in connection therewith for making suitable corrections for magnetic declination or variation so that a dial compass card or. other means controlled by the true north follower I0! will follow the true north rather-than the magnetic north and will always indicate or follow the true directions. The true north follower IGI thus cooperates with the master compass I00 to provide visual means for always indicating true direction irrespective of turning of the vehicle'on which the apparatus is carried, and provides control means for instruments wher directional control is required. I

The true north follower IiII is used to'operate repeater motors at any desired location on the vehicle. These repeater motors operat in exact synchronism with the true north follower as hereinafter explained, and they may beused to operate any desired mechanism. In Fig. 4 I have shown the true north follower as electrically connected with a repeater compass I02 and with automatic control means I03 for the vehicle. The'repeater compass I52 "preferably will give the same true directional readings as the dial 1 means that is operated directly by the true north follower. The automatic control means may be any desired form of directional control such for instance as steering or other means 96 for holding an airplane or ship on a predetermined course.

The true north follower mechanism I0l is also electrically connected with a north and south air speed device IE4 and an east and west air speed device I05. These air speed devices I04 and I55 are for use particularly on air craft and are preferably positioned on parts of the craft where they are exposed to the true north and south components and east and west components respectively of air velocity. The true north follower serves to control, through follower means, the directional positioning of small vanes on these air speed devices. Preferably the vane on the north and south air speed device E55 is positioned and maintained by the truenorth follower in an east and west plane and the vane on the east and west follower is positioned and maintained in a north and south plane as more fully hereinafter explained in connection with these devices.

Two manually operated wind velocity dials or indicators I 06 and I U? are rovided for use in connection with the two air speed devices I04 and I05 respectively. The wind velocity device IE6 is a north and south device adapted to be set manually to indicate the north or south component of wind velocity as ascertained ordinarily from a ground station. The wind velocity device III-7 is an east and west device adapted to be set manually to indicate the east and west component of wind velocity, as ascertained ordinarily from a ground station. The information, as usually obtained from the ground, is used as a basis to Work from but it may be inaccurate and is corrected for error after the device is in operation as hereinafter explained.

The north and south air speed device I84 and the north and south wind velocity device I06 are electrically connected, by repeater mechanism hereinafter described, with a light controlled electrically actuated algebraic totalizer I88 which is. preferably operative to provide arithmetical scale values in the form of electrical impulses that are representative of the al ebraic sum of the two variable quantities from the devices I04 and IE6. These scale valuesmust be converted into motion in a scale-to-motion device I89 before they can be used along with other motion values from a north and south manual map mover III! in another'algebraic-sumdevice I I I. The manual map mover H6 is controlled frompush button switch means I'I 2I I3.

The scale-to-motion device I09 has a constant speed motor 55!) connected therewith. The algebraic sum in the form of electrical impulses from device III is used to operate a north and south map mover H4.

The cast and west air speed device I05 and the east and west wind velocity device III'I are electrically connected by suitable repeater mechanism with an algebraic-sum device II5. This device H5 is operative to provide arithmetical scale values in the form of electrical impulses representative of the algebraic sum of the two variable quantities from the devices I05 and I01. These scale values must be converted into motion before they can be used and this is done in the scaleto-motion device H6. The sum from the scale-to-motion device Ht together with other motion values from an east and west manual map-mover I H, are brought together in another algebraic-sum device II8. Suitable switch buttons II9I2 5 marked E and W, Fig. 1, to designate east and west are provided for controlling the manual map mover I IT. A constant speed motor 550 is connected with the scale-tomotion device H6. The sum from the algebraicsum device II8 is used to operate an automatic east and west map-mover I2 I.

From the above description it will be seen that the north and south controls shown at the left in Fig. 4 and east and west controls shown at the right in Fig. 4 are similar.

The algebraic sums, as represented by electrical impulses from the algebraic totalizers I68 and I I5 respectively, are also connected to suitable repeater motors that control the movement respectively of a north and south direction finder and ground-speed device 94 and an east and west direction finder and ground-speed device 95.

The two devices 94 and 55 control light means and this controls the movement of a direction plate motor 254. Also it controls a scale-tologarithm device 99 and the scale-tologarithm device 99 controls the operation'of a dial-moving device 98 which moves a dial that registers the ground speed, such as miles per hour.

Aside from the devices that are electrically interconnected as hereinbefore described I provide and show on the diagram in Fig. l manuallycontrolled plate-elevating means I22 controlled by push buttons I23 and operated by an elevating motor I24 to elevate the map plate and the distance plate that carries the scale of miles or other units of distance, proportionately.

Also I provide a fixed air-speed device I25 positioned on an air vehicle where it will be exposed to the full velocity of the air passing the vehicle and connected with a suitable scale-to-log device I26 for converting the reactions of the air-speed device I25 into a logarithmic scale which, in turn, actuates the air speed dial I27 on the instrument.

The instruments and map thus briefly described will provide substantially all of the map information required or needed by a pilot to operate an air craft. The instruments give him th air speed, the ground speed, the components of wind velocity and show him the actual direction in which his ship is traveling relative to the true cardinal directions thus affording him cardinal orientation. The map showshim the exact position of his ship relative to the ground at all times.

Cardinal orientation, as used throughout this specification and in the concluding claims, unless otherwise expressly stated, is defined for the purposes hereof as congruence of cardinal directions between the map, or it image on the view plate,

- compass.

and the earths surface. Thus, when a cardinally oriented map or its image is placed horizontally,

Master magnetic-compass and true-fior'th I follower Referring to Figs. to 11 inclusivel show a master magnetic-compass and true-north follower, designated on Fig. 4 as I00 and IOI respectively, comprising a housing formed of a cylindrical shell I connected with a topflange I 3I and having a removable bottom I32. A relatively strong heavy and preferably transparent cover plate I33 is provided in the top of the housing. The cover plate I33 rests on a gasket I34 that is supported on a shoulder I35 of the housing.

A suitable gasket I36 provides a seal between the cylindrical shell I30 and the bottom member All housing parts are preferably non-magnetic and are air tight andthe bottom member I32 and cover plate I33 are hermetically sealed around the edges by the gaskets I34 and I36 thus providing a chamber in which a vacuum may be drawn. The operating arts of the compass are mounted within this vacuum chamber. Iron magnetic shields may be used where desired.

The magnetically actuated part of the compass comprises a magnetic member I31 disposed within an inverted cup-shaped member of non-magnetic material. Preferably the magnetic member I31 is of the usual bar or needle shape and corresponds to the magnetic needle of an ordinary The non-magnetic cup-shaped, member is composed of a plate-like end portion I38 and a cylindrical side wall portion I 39. The side wall portion I39 forms a light shutter-as hereinafter explained. V

Atubular hub member I40 is secured to the end portion I38 of the cup-shaped member axially thereof and extends downwardly therefrom at right angles to said end portion I38. The magnetic member I31, see Fig.- 6, extends through hub member I40.

The hub member I40 preferably has a cross sectional shape of substantially three-quarters of a circle, as shown in Fig. 6. A screw cap MI is provided on the bottom end portion of hub member I40. An internal flange I11 is preferably provided within screw cap I4I to prevent collapse of the hub member I40 when the cap is tightened thereon.

The shutter ring I39, Figs. 5, 6 and 7,- has a plurality of light apertures I provided therein. I have shown a shutter ring I39 formed of material impervious to light and having light apertures I50 in the form of holes therein but obviously this shutter ring may be made of light conductive material painted or coated soas to leave light apertures in the form of light conductive sections instead of the holes I50;

I have shown three annular rows of the light apertures I50 and have shown said apertures I50 to be offset relative to each other transversely of the shutter rings I39 so that the apertures appear to be in slightly inclined rows transversely ofthe shutter ring. The relative positions of these apertures may be varied as long asan arrangement of said apertures is maintained so that light may pass through only one aperture at a time and may pass through said apertures in proper succession.

Three photo-electric cells I5I, I52 and I53 are supported in a common axial plane by the frame I30 in close proximity to the outer circumference of the shutter ring I39. One of the cells I5I, I52 and I53 is positioned in alignment with each annular row of light apertures I'50.

A source of light is positioned within the shutter ring I39 directly opposite the photo-electric cells I5I, I52 and I53.

Preferably this source of light comprises a housing I54 having a plurality of lamps I55 therein and having a narrow upright slot I56 positioned close to the inside of the shutter ring I39 and directly opposite the photoelectric cells I5I, I52 and I53. I

The rear wall of the housing I54 is preferably of concave shape and the walls of said housing are mirrored so as to reflect the light forwardly and concentrate this re'flected light at the location of the slot I56. I

The photo-electric cells I5I, I52 and I53 act as electric valves which permit a flow of electric current therethrough when a beam of light is incident thereon and shut off the flow of electric current when no light is incident thereon.

Each photo-electric cell I5I I52 and I53 is connected by a common circuit wire I51 with a source of supply of electric current, such as a battery I58. Also said photo-electric cells I5I, I52 and I53 are connected by circuit wires I59, I60 and I6I with sets of coils I62, I63 and I64 of a repeater type electric motor shown diagrammatically in Figs. 8, 9 and 10.

I have shown a repeater type electric motor I14 with six equidistantly spaced pole pieces I65 gach embodying a north and a south pole, see

The sets of coils I62, I 63 and I64 each consist of four coils disposed two each on diametrically opposite pole pieces, i.,e., two of the coils I62 are wound in opposite directions on one pole piece I65, as shown in Fig. 9, and the other two coils I62 are wound on the diametrically opposite pole piece I65, see Fig. 8. Thus each pole piece I65 is provided with a north and south pole.

The rotary portion of the motor consists of two horseshoe type preferably permanent magnets I66 and I61 rigidly secured together in back to back relation and extending in opposite directions as shown in Figs. 8 and 9. A strip of insulating material I68 is preferably provided between the two magnets I66 and I61. The magnets I66-I61 are journaled in bearings I69 and have a gear pinion I10 connected therewith. Obviously the permanent magnets I66 and I61 may be electromagnets if desired.

The closing of the electric circuits through the sets of coils I62, I63 and IE4 is controlled by the respective photo-electric cells I5I, I52 and I53 in response to relative movement between the cylindrical light shutter I39 and the photo-electric cells and light source.

As the shutter I39 and photo-electric cells and light source relatively move rotatively the light will fall on the photo-electric cells successively thus successively energizing the different sets of coils I62, I63 and I64. If the shutter ring I39 moves in one direction relative to the source of light such as clockwise as respects the showing in Fig. 6 (this being equivalent to moving the shutter I39 to the left or the light source to right as respects the showing in Fig. '2), then the photoelectric cells will be exposed in the order II- I52--I53 and the magnet coils will be energized in the order I62I63-I64, and the device will repeat in this order as long the shutter ring continues to relatively move in the same direction. This will rotate the "magnets IE6 and I61 in a clockwise direction as respects Figs. 8 and 10.

If the shutter ring I39 relatively moves in the opposite direction, then the order in which the circuits through the coils will be closed will be reversed and the order in which the energizing of the coils will be repeated will be I64I03-I62. This will rotate the magnets I66 and I61 counterclockwise, as respects the showing in Fig. 8.

The gearwheel I41 that carries the bracket I46 and bearing pin I42 is controlled by a repeater motor I14 of the type shown in Figs. 8 and 9. The repeater motor I 14 is positioned within the housing I30 and the gear pinion I10 of said motor is meshed with the gearwheel I 41.

The repeater motor I14 is electrically connected with the photoelectric cells I 5| I52 and I53 in such a manner as to always provide rotation of the follower mechanism in the same direction and at the same angular velocity as the magnetic member I31.

In this connection it is to be remembered that rotary movement of the magnetic member is a movement relative to the housing I-I3 I-I32 and that the magnetic member really tends to remain in a fixed or magnetic north position while the housing moves rotatively relative to this member.

When relative movement in one direction between the housing and the magnetic member starts it will only have to change the relative position of the shutter ring I39 enough to obstruct the light from one photo-electric cell and allow light to fall on the next cell to cause the follower mechanism to start to follow the magnetic member. As long as the relative movement between the housing and the magnetic member continues the follower mechanism will follow the magnetic member and the rotary movement will take place on the bearing I49 thereby relieving the more delicate bearings I43M4 of substantially all frictional resistance and wear. When the magnetic member comes to rest relativeto the housing the follower mechanism will also come to rest.

If the relative direction of movement of the magnetic member and housing is reversed, the follower mechanism will follow the magnetic member in the new direction.

Slight variations or fluctuations of the magnetic member are taken care of on the needle point or jewel bearings 143-144 without starting operation of the following mechanism.

To obviate all possibility of the magnetic merhher 531 being influenced by electromagnetic lines of force emanating from the motor I14 I preferably provide a shield for this motor such as an annular soft iron housing I10 of inverted U-shape in cross section. This housing I13 is coaxial relative to the magnetic member 31 so that if any magnetism emanates from the motor 514 it will be uniformly distributed by the housing 10 and will not cause any deviation of the magnetic member 131. It is obvious that any other magnetic screening means may be employed, such as to arrange the follower motor control of the 1'0 device so that its axis is coincident with the axis of the device and gear I41 is driven by a planetary train of gears therefrom.

As the lamps I and electric repeater motor I14 will necessarily give off some heat and as a vacuum is preferably drawn within the compass housing I preferably provide cooling means for taking care of this heat. This cooling means preferably consists of a cooling-liquid conduit 519 which extends through the walls of the housing member I30 and is coiled about a metal bracket I80. The metal bracket I 80 is of high thermal conductivity and is connected with both the motor I14 and the lamp housing I54 so that heat from both the motor I14 and housing I54 are drawn off rapidly.

The liquid conduit members I19 are brazed or otherwise sealed where they pass through the wall of housing member I30.

The disc I38 may have suitable graduations printed on its top surface which are visible through the glass cover plate I33 to give the desired compass reading. This reading will give the magnetic north rather than the true north.

Permanent-adjustment between the disc I33 and magnetic member i31 may be made at the time the compass is assembled to take care of any magnetic deviation existing due to magnetism other than the earths magnetic field, particularly magnetism inherent in the device or vehicle on which it is mounted.

Fig. 10 is a diagrammatic view of repeater mechanism using the motor shown in Figs. 8 and 9 for operating a dial which may be located at a point remote from the compass shown in Fig. 5.

In said Fig. 10 the photo-electric cells I5I, I52 and IE3 and circuit wires I51, I 59 and I60 and IEI and coils I02, I63, and I64 and magnets I66 and I61 are all shown diagrammatically.

Another pinion I13, on another similar repeater motor I14, connected with similar magnets I66 and IE1, meshes with gearteeth I1! on a flange I12 of a magnetic-north indicator ring I13, Fig. 10.

The ratio of the gears He and I12 is such as to provide movement of the magnetic north indicator ring I13 in exact synchronism with the movement of the magnetic member I31 and the disc or dial member I38.

Obviously as many as desired of the repeaters of the type shown in Figs. 8, 9 and 10 may be 0perated from the photo-electric cells I5I, E52 and When the compass shown in Figs. 5 to 10 is in use the magnetic member I 31 will seek a position in which it will point to the magnetic north. This magnetic member will always be free to move in vacuum on the needle point or jeweled bearings which oifer the least possible amount of frictional resistance. Immediately after relative movement between the magnetic member I31 and the housing commences, the circuits to the magnet coils of the repeater motor I14 are successively closed and the follower mechanism follows the magnetic member so that there is no further movement on the needle point or the jeweled bearings. If movement between the magnetic member I31 and housing I30 slows down or stops or reverses in direction the follower mechanism does the same, as it is controlled by the passage of light through the openings 50 in the shutter I39 and the shutter I39 is controlled by the magnetic member I31.

The compass is thus very accurate and very reliable and very durable. The bearing I49 that carries the follower mechanism is strong and substantial and will last indefinitely. The bearings on which the magnetic member I31 depends for its sensitivity are substantially frictionless and are only subjected to a very slight amount of wear.

The repeater mechanism is controlled by the magnetic member without any actual contact of moving parts and for this reason does not detract from the sensitivity of the magnetic member. The repeater motors that are controlled by the photo-electric cells derive their current from an external source and are reliable and efficient. As many of these repeater motors as may be desired can be operated from a single set of photoelectric cells.

The mechanism is all sealed in a substantial vacuum thereby safeguarding this mechanism against dirt in all forms, moisture and corrosion. Also sealing this mechanism in a vacuum safeguards it against the action of air resistance.

The master magnetic compass may be located on any part of the vehicle. The conductors I51, I59 and I99 and I8I from the photo-electric cells II, I52 and IE3 extend to the magnetic-north follower-motor shown diagrammatically in Fig. 10. This magnetic-north follower-motor, shown diagrammatically in Fig. 10 is mounted within the housing I shown in Fig. 11 with its pinion I18 meshed with the gearteeth I1I provided on the flange I12 of the cylindrical magnetic-north indicator ring I13. The upper edge portion of the ring I13, Fig. ll, is preferably flush with the top surface of a map stand or instrument board I8I which is fixed relative to the instrument and carries a ships heading index mark 9I.

Parts I12-I13, Fig. 11, are journaled in a downwardly extending flange I82 of board I8I by a bearing I83.

A rotatable true-north dial I84, Fig. 11, of annular shape is positioned just within the flange I82 and rigidly connected with a rotatable hous-' ing member I85. Parts I84 and I85 are also supported by bearing 83.

A thumb turn wheel I89 is rotatively mounted on a bearing member I81 that is rigid with the housing member I85 and projects outwardly therefrom. A friction member I88 yieldingly engages the thumb wheel I89 to prevent accidental or vibratory turning thereof.

The upper portion of the thumb wheel I88 eX- tends through a slot I89 in the true north dial I84into a position where it may be conveniently engaged by the thumb or finger of the operator for turning the same.

The thumb wheel I86, Figs. 1 and 11, has a gear means I99 thereon that meshes with another gear means I9I on the magnetic north indicator ring I13.

The magnetic north indicator ring I13 has a reference mark I92 thereon as shown in Fig. 1, that always indicates magnetic north. The true north dial I84 is preferably graduated in degrees as shown in Fig. 1.

The housing I85 is rotatably supported by the bearing I83 and by other means hereinafter described, and the thumb wheel I96 and gear means I 99 and I91 serve as adjustable means for securing the rotatable housing member I85 to the magnetic north indicator ring I13 so that these two parts ordinarily move as one unit.

' However when they move relative to each other by operation of thumb wheel I89, mating surfaces 12 I28 and shoulders I29 between members I and I13 provide the necessary bearing engagements; The magnetic declination or variation at different locations on the earth as known and readily available in table and chart form and adjust'm en't for this magnetic declination orivariationcan be made by turning the thumb wheel The motor housing I 15 is preferably secured'to a bracket 293, Fig. 11, that is connected "with the instrument board I8I by a pivot 294 and a screw 295.

By loosening thescrew 285 the pinion I19 may be moved about pivot 204 out of mesh with the gear HI and the-magnetic north follower elements I12-I13 adjusted to bring it into correct step with the compass'that it is to follow.'

Throughout the drawings I have shown batteries I58 as illustrative of a source of electrical energy. All of these batteries are numbered I58. It will be understood that any suitable source of current may be used instead of these batteries, or one battery may serve for a group or all.

Main map stand and housing means The main map stand and housing means, see Figs. 1, 2, 3, 11, 12, 13, 14 and 15 has a face comprising an instrument'board I8I shown in Fig. 1 which includes the parts I13, I8I, I84 and I85 just hereinbefore described.

. The vertical in Fig. 1, passing through center 99 and index mark 9|, is parallel with the fore and aft axis of the craft and mark 9| indicates the line of apparent direction or heading of the craft which is read on the scale of dial I84 while distance and direction scale 25I shows the real line of movement of the craft and the angular difference about center between scale 25I an mark 98 shows the wind drifts.

The instrument board I8I, Fig. 2, supports an outer fixed cylindrical housing I93. The housing I93 has an annular bottom member I94 preferably formed of electrical insulating material and this bottom member I94 is centrally provided with a downwardly extending cylindrical receptacle I95 also preferably formed of electrical insulating material.

The rotary housin part I85 is disposed within the fixed housin I93, Fig. 2, and is secured by means such as screws or rivets I96 to a lower housing part I91. The lower housing part I91 has a bottom I98. Parts I91 and I98 are preferably formed of electrical insulating material.

A light projector housing I99, Fig. 2, extends through a suitable opening in the bottom I98 of the rotatable housing member I 91 and is secured thereto by means such as a nut 290 that securely clamps the bottom member I98 against a shoulder 20I on the projector housing I99. The projector housing I99 is journaled in a bearing member 292 in the bottom of the well portion I 95. The bearing member 292 rotatively supports the lower end portion of the housing I99--I98 HIT-I85 and the upper end portion thereof is rotatively supported by the bearing member J83: 

